Evaluating the impact of eligibility for free care on the use of general practitioner (GP) services: A difference-in-difference matching approach

In Ireland, approximately 30% of the population ('medical card patients') are entitled to free general practitioner (GP) care while the remaining 70% ('private patients') must pay the full cost of each visit. Previous research has analysed the effect of this system on GP visiting patterns using regression methods, but to date, no attempt has been made to apply techniques from the treatment evaluation literature to this issue. Treatment evaluation techniques are commonly employed when observations are not randomly assigned to treatment and control groups; this is certainly the case here, as the primary criterion for medical card eligibility is an income below a specified income threshold (and individuals may also be granted medical cards for other reasons such as chronic ill-health). In this paper, previous Irish research, which has analysed the effect of medical card eligibility on GP visiting using regression methods, is extended to consider the use of difference-in-difference matching methods, which control for non-random selection into treatment and control groups, as well as differences in time-invariant unobserved characteristics between individuals in both groups. The results are largely consistent with earlier results using pooled cross-sectional and panel data, and confirm that medical card eligibility exerts a significant effect on GP visiting, even after controlling for observed and unobserved differences in characteristics between medical card and private patients.